Influence of cerium salt concentration, co-solvents and water on the efficiency of supercritical CO2 extraction

The extraction of cerium from cotton substrate, as a matrix model, using supercritical CO2 modified with phosphorus extractant and co-solvent/water in wise proportions, has been investigated. Using a recently developed isobutyl amidophosphonate extractant, the aim of this study was to emphasize how besides the usually considered operating parameters (flow rate, pressure and temperature), the efficiency of supercritical CO2 extraction of cerium depends on the concentration of cerium nitrate deposits on the substrate (between 0.27 and 261 mg gcotton(-1)) and on the presence and composition of co-solvent/water mixture as well. The variations of the extraction efficiency with the nature of the Ce nitrate deposits (aggregates or homogenous layers) are explained by using a deposition model confirmed using SEM and coupled with SAXS data. Extraction is promoted when Ce nitrates deposits are in the form of segregated aggregates instead of homogeneous layers. Phase equilibrium data for CO2-ethanol-amidophosphonate and CO2-isopropanol-amidophosphonate ternary systems have been measured at 40 degrees C and 25 MPa to investigate the benefit of using a co-solvent. Extraction experiments show that adding a co-solvent and carefully adjusting the water concentration up to 30%wt are crucial to obtain high mass extraction yields, here up to 82%. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.